Don't Let Yourself Get Tricked!

Algebra

I'm sitting in a room at $20^{\circ}C$ when all of a sudden it warms to $40^{\circ}C$ .

What is the percent change, to the nearest integer, in the temperature $T$ ?

Details & Assumptions:

The formula for percent change between $x_{1}$ and $x_{2}$ is $\Delta$ % $= 100\large{\frac{x_{2}-x_{1}}{x_{1}}}$ .

None of These! 53% 19% 100% -24% 7% 0%